Stereo vision techniques have been used for detecting obstacles, such as people. In this technique, disparity is calculated by calculating corresponding points using a correlation operation from camera images on either side. Three-dimensional coordinates of the obstacles are calculated from the calculated disparity, and the objects are detected from height information. However, it is not easy to calculate disparity correctly due to an influence of lighting or weather changes.
JP-A 2006-53890 (KOKAI) discloses an apparatus and a method for obstacle detection which apply a plane projection stereo method as a robust technique against lighting or weather changes. According to JP-A 2006-53890 (KOKAI), a projection parameter is calculated beforehand based on camera images on either side such that positions of points on a road surface in one image corresponds to those on a road surface in the other image. The point set on the road surface of one image, which corresponds to the point on the other image, is calculated based on the calculated projection parameter. Transformed image approximated to one image is created using a relation of the corresponding points. The objects which have a size greater than a certain size in perpendicular above direction with respect to a road plane are detected using the corresponding points and the transformed image.
In this technique, cameras on either side are arranged in the similar height as those of the obstacles, and it is assumed that the depression angle is small. According to this technique, only the boundary line between one obstacle and a road surface with respect to the perpendicular direction of a camera image can be detected. In a case where cameras are arranged in a high position with respect to obstacles and a plurality of obstacles need to be detected in the perpendicular direction of the camera image, the function may not be realized.